Intermittent Limit Switch Issue.

Goodman GUPI100-4 gas furnace.

Original call, no power, blown transformer, installed new. Next day call back, outside unit not running. No led, btw. Inducer and blower on only while on call for cool. Check for 24 to ground on secondary limit terminals (limit hooked to board) and good to go, continuity, closed. Primary limit nothing. Pull switch wires off of board and check to ground, one shows 24 volts, 26.2 actually but that's irrelevant, and the other spade on the board shows nothing.

Brand new gator clip, jumped from terminal to terminal and limit switch loop still open..?? Brand new control board, too, I should mention. Actually two new boards, Goodman tech support said the first brand new board (I thought original existing board was bad as with limit loop jumped on original board it was still acting like it was open, inducer and blower on only) was bad so I got another one. Today, with second new board in place, they had me remove 24 volts from stat and said if the system turned off the stat was the problem. It powered off so I changed the stat, same issue.

They were also talking about taking the 24 volt transformer common to furnace chassis before telling me the stat was bad which I have not done, yet.

Intermittent Limit Switch Issue.

check the wiring diagram on the back of one of the doors or get one from Goodman. must have some mixed up wiring. may have some mixed up wiring to the tstat or pinched/shorted to it. if R and W get mixed up the heat can still work but no AC. sounds more like a bad wiring to the tstat issue 2 me. I have had pinched wiring get bare and hit metal ducts and have intermittent shorts or cats chew it etc etc. may need a new wire to the tstat.

Intermittent Limit Switch Issue.

The polarity thing is one thing I did not check nor did I ever ground the transformer common. No matter, another company and another tech from my company both could not figure it out so they're getting a new furnace.

Intermittent Limit Switch Issue.

Quote:

Originally Posted by Doc Holliday

The polarity thing is one thing I did not check nor did I ever ground the transformer common. No matter, another company and another tech from my company both could not figure it out so they're getting a new furnace.

Better hope it isn't a problem back at the panel box. or the new furnace may not work either.

Intermittent Limit Switch Issue.

keep in mind the solid state board needs to see a sequence on HEAT call IDF blower ON, Pressure switch closes spark then the burner runs...jumping the switch confuses the board in the heat cycle call..jump it right after the IDF starts..

Intermittent Limit Switch Issue.

The problem could be a poor connection in one of the molex plugs if it had them. Sometimes they don't seat properly or get corroded. Have to pull them apart and examine them with a magnifying glass and reseat them properly. Good chance that unit had popped compression rings in the heat ex if it was one of them. Goodmans can be a bit different as they put the limit in series with the gas valve on the newer ones. Jobs like that can drive a person CRAZY

Intermittent Limit Switch Issue.

Intermittent Limit Switch Issue.

Go to the control tab on the right side and click it. Then click settings. Scroll down to passwords and forms. Click manage saved passwords. Then when the new box opens, scroll to DIYCHATROOM, click it, then click show. To show you the password.